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[Merged by Bors] - feat(normed_space/inner_product): euclidean_space.norm_eq #6744

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@pechersky pechersky added awaiting-review The author would like community review of the PR easy < 20s of review time. See the lifecycle page for guidelines. labels Mar 17, 2021
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Can we try to do this by fixing the diamond?
https://leanprover.zulipchat.com/#narrow/stream/116395-maths/topic/.60inner_product_space.20.E2.84.9D.20(euclidean_space.20.F0.9D.95.9C.20n).60.3F

I think that's the more natural approach.

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I'm only adding the lemma that expands out the norm for a term of the euclidean space. I think fixing the diamond might have to do with how the semimodules are defined differently on the different type wrappers.

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Ah, I see. Can you please give this lemma for pi_Lp 2 one_le_two, similar to pi_Lp.inner_apply, and deduce the euclidean_space version from it? (At that point the euclidean_space version may not even be needed, since it is definitionally a pi_Lp.)

@kim-em kim-em removed the easy < 20s of review time. See the lifecycle page for guidelines. label Mar 18, 2021
@@ -229,6 +229,11 @@ lemma norm_eq {p : ℝ} {hp : 1 ≤ p} {α : ι → Type*}
[∀i, normed_group (α i)] (f : pi_Lp p hp α) :
∥f∥ = (∑ (i : ι), ∥f i∥ ^ p) ^ (1/p) := rfl

lemma norm_eq_of_nat {p : ℝ} {hp : 1 ≤ p} {α : ι → Type*}
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I added this lemma because of the notational confusion between ^ when encoding rpow or monoid.pow. For working with nat powers, this will allow for cleaner rewrites, with easy discharging with norm_num. I couldn't figure out how to use . tactic.norm_num as the out_param there.

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I added this lemma because of the notational confusion between ^ when encoding rpow or monoid.pow. For working with nat powers, this will allow for cleaner rewrites, with easy discharging with norm_num. I couldn't figure out how to use . tactic.norm_num as the out_param there.

This seems reasonable to me, but I'd like someone like @sgouezel who's been involved in the design of the L^p spaces to decide about this, in case there's a reason we haven't had lemmas like this already.

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Co-authored-by: hrmacbeth <25316162+hrmacbeth@users.noreply.github.com>
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bors r+
Thanks!

@github-actions github-actions bot added ready-to-merge All that is left is for bors to build and merge this PR. (Remember you need to say `bors r+`.) and removed awaiting-review The author would like community review of the PR labels Mar 18, 2021
bors bot pushed a commit that referenced this pull request Mar 18, 2021
Co-authored-by: Yakov Pechersky <pechersky@users.noreply.github.com>
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bors bot commented Mar 18, 2021

Pull request successfully merged into master.

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@bors bors bot changed the title feat(normed_space/inner_product): euclidean_space.norm_eq [Merged by Bors] - feat(normed_space/inner_product): euclidean_space.norm_eq Mar 18, 2021
@bors bors bot closed this Mar 18, 2021
@bors bors bot deleted the pechersky/eucl-norm-eq branch March 18, 2021 23:42
b-mehta pushed a commit that referenced this pull request Apr 2, 2021
Co-authored-by: Yakov Pechersky <pechersky@users.noreply.github.com>
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